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This post was last edited by Su Ya on 2021-7-2 10:45 1. What is a pump? 1. Pumps are mainly used to transport liquids such as water, oil, acid and alkali liquids, emulsions, suspoemulsions and liquid metals. Gear oil pumps can also transport liquid and gas mixtures and liquids containing suspended solids. 2． Pumps can usually be divided into three categories: positive displacement pumps, dynamic pumps and other types of pumps according to their working principles. In addition to being classified according to working principles, submersible pumps can also be classified and named according to other methods. For example, according to the driving method, it can be divided into electric pump and water wheel pump, etc. ； According to the structure, it can be divided into single-stage pump and multi-stage pump. ； According to use, it can be divided into boiler feed water pumps and metering pumps, etc. ； According to the properties of the transported liquid, it can be divided into water pumps, oil pumps and mud pumps, etc. 3． There is a certain interdependence and changing relationship between various performance parameters of the pump, which can be represented by drawing a curve, which is called the characteristic curve of the pump. Each pump has its own specific characteristic curve. A pump is a machine that transports liquid or pressurizes liquid. It transfers the mechanical energy of the prime mover or other external energy to the liquid, increasing the energy of the liquid. 2. The definition and historical origin of a pump is a machine that transports liquid or pressurizes liquid. A pump in a broad sense is a machine that transports fluid or pressurizes it, including some machines that transport gas. The pump transfers the mechanical energy of the prime mover or the energy of other energy sources to the liquid, thereby increasing the energy of the liquid. The improvement of water is very important for human life and production. There have been various water-lifting devices in ancient times, such as the Egyptian chain pump (17th century BC), the Chinese tangerine (17th century BC), the windlass (11th century BC), the waterwheel (1st century AD), and the screw rod invented by Archimedes of ancient Greece in the 3rd century BC. Around 200 BC, the ancient Greek craftsman Ctesibius invented the most primitive piston pump-the fire extinguishing pump. As early as 1588, there were records of a 4-vane sliding vane pump, and various other rotary pumps appeared one after another. In 1689, D. Papin of France invented the volute centrifugal pump with a 4-blade impeller. In 1818, a centrifugal pump with radial straight blades, semi-open double-suction impeller and volute appeared in the United States. From 1840 to 1850, HR Worthington of the United States invented a piston pump with direct steam action in which the pump cylinder and the steam cylinder were opposite, marking the formation of the modern piston pump. From 1851 to 1875, multi-stage centrifugal pumps with guide vanes were invented one after another, making it possible to develop high-lift centrifugal pumps. Subsequently, various pumps came out one after another. With the application of various advanced technologies, the efficiency of pumps has gradually improved, and the performance range and applications have also expanded. 3. Pumps are classified according to the various types of pumps, which can be divided into: ①Dynamic pumps, also called impeller pumps or vane pumps, fire pumps rely on the dynamic effect of the rotating impeller on the liquid. The submersible pump continuously transfers energy to the liquid, increasing the kinetic energy (mainly) and pressure energy of the liquid. The kinetic energy is then converted into pressure energy through the extrusion chamber. It can be divided into centrifugal pumps, axial flow pumps, partial flow pumps and vortex pumps, etc. ②Positive displacement pumps rely on periodic changes in the volume of the sealed working space containing the liquid to periodically transfer energy to the liquid, increasing the pressure of the liquid to the point where the liquid is forcibly discharged. According to the movement form of the working element, it can be divided into reciprocating pumps and rotary pumps. ③Other types of pumps deliver energy in other forms. For example, a jet pump relies on high-speed injection of working fluid to suck the fluid to be transported into the pump and then mix it, exchanging momentum to transfer energy. ； Diaphragm pump water hammer pump uses part of the flowing water to be raised to a certain height during braking to transfer energy. ； The electromagnetic pump makes the energized liquid metal flow under the action of electromagnetic force to achieve transportation. In addition, pumps can also be classified according to the nature of the liquid transported, driving method, structure, use, etc. 4. Application of Pumps in Various Fields Judging from the performance range of the pumps, the flow rate of giant pumps can reach more than hundreds of thousands of cubic meters per hour, while the flow rate of metering pumps and micro pumps is less than tens of milliliters per hour. ； The pressure of the pump can range from normal pressure to over 19.61Mpa (200kgf/cm2) ； The temperature of the transported liquid can reach as low as -200 degrees Celsius and as high as over 800 degrees Celsius. Pumps transport a wide variety of liquids, such as water (clean water, sewage, etc.), oil, acid and alkali liquids, suspensions, and liquid metals. In the production of the chemical and petroleum sectors, raw materials, semi-finished products and finished products are mostly liquids. Fire pumps are required to make semi-finished products and finished products from raw materials through complex processes. In these processes, pumps play the role of transporting liquids and providing pressure flow for chemical reactions. In addition, pumps are also used in many devices to regulate temperature. In agricultural production, pumps are the main drainage and irrigation machinery. my country's rural areas are vast and require a large number of pumps every year. Generally speaking, agricultural pumps account for more than half of the total pump output. In the mining and metallurgical industries, pumps are also the most used equipment. Mines need to be drained by pumps, and pumps are needed to provide water during the mineral processing, smelting and rolling processes. In the power sector, nuclear power plants require nuclear main pumps, secondary pumps, and tertiary pumps. Thermal power plants require a large number of boiler feed water pumps, condensate water pumps, circulating water pumps, and ash pumps. In national defense construction, pumps are required for the adjustment of aircraft flaps, tail rudders and landing gear, the rotation of warship and tank turrets, and the ups and downs of submarines. High-pressure and radioactive liquids, some also require the pump to have no leakage, etc. In the shipbuilding industry, there are generally more than a hundred pumps used on each ocean-going ship, and their types are also various. Others, such as urban water supply and drainage, water for steam locomotives, lubrication and cooling in machine tools, transporting bleach and dyes in the textile industry, transporting pulp in the papermaking industry with self-priming pumps, and transporting milk and sugary foods in the food industry, etc., all require a large number of pumps. In short, whether it is airplanes, rockets, tanks, submarines, drilling, mining, trains, ships, or daily life, pumps are needed everywhere and pumps are running everywhere. This is why pumps are classified as general machinery, and they are an important product in the machinery industry. 5. Basic parameters of the pump The basic parameters of the main performance of the pump are as follows:: 1. Flow Q Flow is the amount of liquid (volume or mass) delivered by the pump per unit time. The volume flow rate is expressed by Q, and the unit is: m3/s, m3/h, l/s, etc. The mass flow rate is expressed by Qm, and the unit is: t/h, kg/s, etc. The relationship between mass flow rate and volume flow rate is: Qm=ρQ where ρ——density of liquid (kg/m3, t/m3), normal temperature clear water ρ=1000kg/m3. 2. Lift H Lift is the added value of energy per unit weight of liquid pumped by the pump from the pump inlet (pump inlet flange) to the pump outlet (pump outlet flange). That is the effective energy obtained by one Newton of liquid through the pump. Its unit is N·m/N=m, which is the height of the liquid column of the liquid pumped by the pump. * Commonly referred to as meters. 3. Speed n Speed is the number of revolutions of the pump shaft per unit time, represented by the symbol n, and the unit is r/min. 4. Cavitation headroom NPSH cavitation head, also called net positive suction head, is the main parameter indicating cavitation performance. The NPSH has been expressed as Δh in China. 5. Power and efficiency The power of a pump usually refers to the input power, that is, the power on the pump shaft of the prime mover, so it is also called shaft power, represented by P. ； The effective power of the pump is also called output power and is represented by Pe. Diaphragm pump is the effective energy obtained in the pump by the liquid delivered from the pump per unit time. Because the head refers to the effective energy obtained from the pump per unit weight of liquid output by the pump, the product of the head, mass flow rate and gravity acceleration is the effective energy obtained from the liquid output from the pump per unit time - that is, the effective power of the pump: Pe=ρgQH(W)=γQH(W) where ρ——density of liquid transported by the pump (kg/m3) ； γ——The gravity of the liquid delivered by the pump (N/m3) ； Q——Pump flow rate (m3/s) ； H——Head of the pump (m) ； g——gravitational acceleration (m/s2). The difference between shaft power P and effective power Pe is the power loss in the pump, and its size is measured by the efficiency of the pump. The efficiency of the pump is the ratio of effective power to shaft power, expressed by eta. 6. What is traffic? What letters are used? How to convert? The volume of liquid discharged by the pump per unit time is called flow. The flow is represented by Q, and the unit of measurement is: Cubic meters/hour (m3/h), liter/second (l/s), L/s=3.6 m3/h=0.06 m3/min=60L/min G=Qρ G is the weight ρ is the specific gravity of the liquid. Example: The flow rate of a certain pump is 50 m3/h. What is the weight per hour when pumping water? The specific gravity of water is 1000 kg/cubic meter. untie: G=Qρ=50×1000(m3/h·kg/m3)=50000kg/h=50t/h 7. What is lift? What letters are used? What unit of measurement is used? and pressure conversion and formula? The energy gained by unit weight of liquid passing through the pump is called head. The lift of the pump, including the suction lift, is approximately the pressure difference between the pump outlet and inlet. The head is represented by H and the unit is meters (m). The pressure of the pump is expressed by P, the unit is Mpa (MPa), H=P/ρ. If P is 1kg/cm2, then H=(lkg/cm2)/(1000kg/m3) H=(1kg/cm2)/(1000kg/m3)=(10000kg/m2)/1000kg/m3=10m 1Mpa=10kg/c m2,H=(P2-P1)/ρ (P2=outlet pressure P1=inlet pressure) 8. What is cavitation margin? What is the suction process? What letters represent the respective units of measurement? When the pump is working, the liquid will generate vapor under a certain vacuum pressure at the inlet of the impeller. The vaporized bubbles will erode the impeller and other metal surfaces under the impact of the liquid particles, thereby destroying the impeller and other metals. At this time, the vacuum pressure is called vaporization pressure. The vaporization margin refers to the excess energy of the unit weight of the liquid at the pump suction inlet that exceeds the vaporization pressure. Units are marked in meters, using (NPSH)r. The suction lift is the necessary NPSH Δh: That is, the vacuum degree that the pump allows to suck liquid, that is, the installation height that the pump allows, in meters. Suction lift = standard atmospheric pressure (10.33 meters) - NPSH - safety amount (0.5 meters). The standard atmospheric pressure energy pressure pipeline vacuum height is 10.33 meters. For example: The required NPSH of a certain pump is 4.0 meters. What is the suction lift Δh? untie: Δh=10.33-4.0-0.5=5.83 m 9. What is the cavitation phenomenon of water pumps and its causes 1. When the cavitation liquid is at a certain temperature and the pressure is reduced to the vaporization pressure at that temperature, the liquid will generate bubbles. This phenomenon of bubble generation is called cavitation. 2. Cavitation collapse: When the bubbles generated during cavitation flow to high pressure, their volume decreases and they burst. This phenomenon of bubbles disappearing into the liquid due to rising pressure is called cavitation collapse. 3. Causes and hazards of cavitation During the operation of the pump, if for some reason the absolute pressure of the pumped liquid drops to the vaporization pressure of the liquid at the current temperature in the local area of the overflow part (usually somewhere behind the impeller blade inlet), the liquid will begin to vaporize there, generating a large amount of steam and forming bubbles. When the liquid containing a large number of bubbles passes forward through the high-pressure area in the impeller, the high-pressure liquid around the bubbles will cause the bubbles to shrink sharply and even burst. When the bubbles in the submersible pump condense and burst, the liquid particles fill the holes at a very high speed. At this moment, a strong water hammer effect is produced, and the metal surface is hit at a very high impact frequency. The impact stress can reach hundreds to thousands of atmospheres. The impact frequency can reach tens of thousands of times per second. In severe cases, the wall thickness will be broken down. 4. The cavitation process in the water pump is the process in which bubbles are generated and the bubbles burst, causing damage to the flow-passing components. This is the cavitation process in the water pump. After cavitation occurs in a water pump, in addition to damaging the flow-passing components, it will also produce noise and vibration, which will lead to a decrease in pump performance. In severe cases, the liquid in the pump will be interrupted and the pump will not work properly. 10. What is the pump characteristic curve? The curve representing the relationship between the main performance parameters is usually called the performance curve or characteristic curve of a centrifugal pump. In essence, the performance curve of a centrifugal pump is an external manifestation of the movement of liquid in the pump and is obtained through actual measurements. Characteristic curves include: Flow-head curve (QH), flow-efficiency curve (Q-η), flow-power curve (QN), flow-NPSH curve (Q-(NPSH)r), and the performance curve can be used at any flow point of the pump. Find a set of corresponding head, power, efficiency and NPSH values online. This set of parameters is called the working state, referred to as the working condition or working point. The working condition at the highest efficiency point of the centrifugal pump is called the best working point, and the best working point is generally the design working point. Generally, the rated parameters of centrifugal pumps, that is, the design operating point and the optimal operating point, coincide with or are very close to each other. Operating within the selected efficiency range in practice not only saves energy but also ensures normal operation of the pump, so it is very important to understand the performance parameters of the pump. 11. What is pump efficiency? formula? Refers to the ratio of the effective power of the pump to the shaft power. η=Pe/P The power of the pump usually refers to the input power, that is, the power transmitted from the prime mover to the pump shaft, so it is also called shaft power and is represented by P. The effective power is: The product of the pump head and the mass flow rate and the acceleration due to gravity. Pe=ρg QH (W) or Pe=γQH/1000 (KW) ρ: Density of liquid delivered by the pump (kg/m3) γ: The weight of the liquid delivered by the pump γ=ρg (N/m3) g: Acceleration of gravity (m/s) Mass flow rate Qm=ρQ (t/h or kg/s) 12. What is a full performance test bench for pumps? The equipment that can accurately test all performance parameters of the pump through precision instruments is a full-performance test bench. * * The standard accuracy is level B. The flow rate is measured with a precision worm gear flowmeter, and the head is measured with a precision pressure gauge. The suction lift is measured with a precision vacuum gauge. Power is measured with a precision shaft dynamometer. The rotational speed is measured with a tachometer. Efficiency is based on actual measured values: n=rQ102 calculation.